This invention relates to graphical digitizer equipment and, more particularly, to improvements in validating and screening measurements obtained from such equipment.
Graphical digitizers are conventionally used to input graphical coordinate information, or the like, to a companion system. In a graphical digitizer, wave energy is typically passed between a movable element (such as a stylus or cursor) and one or more transducers located at fixed reference locations. The transit time of the wave energy traveling (in either direction) between the movable element and the reference locations is used in determining the position of the movable element in one, two, or three dimensions, typically in terms of digital coordinates. A type of graphical digitizer manufactured and sold by the assignee hereof, Science Accessories Corporation, measures the transit time of acoustic or sonic energy propagating through air. The transit time of sound traveling from a source on the movable element to each of a plurality of microphones is used, in conjunction with the velocity of sound in air and known geometrical relationships, to compute the position of the movable element.
Graphical digitizer equipments, like most measuring equipments, are susceptible to errors caused by noise and other factors. For example, through-the-air sonic digitizers of the type described above are susceptible to extraneous acoustic noise in the environment, and also to multipath echoes of the sound energy employed by the digitizer equipment itself. Electronic interference or other intermittent phenomena can also lead to substantial digitizing errors.
Since digitizers are typically utilized to measure and store data points at a relatively high acquisition rate, and since the acquired data is often immediately used by a companion system, the occurrence of occasional inaccurate coordinate measurements, even grossly inaccurate ones, may not be recognized at all, or until they cause a problem in subsequent processing. The outputting of even occasional incorrect coordinate data can be particularly undesirable for certain applications. Further, when subsequent processing involves averaging of acquired data points, a few grossly inaccurate measurements can result in substantial errors in averaged data that would otherwise be quite acceptable.
It is among the objects of the present invention to reduce or eliminate these type of problems in graphical data digitizers and particularly, although not necessarily, in sonic graphical digitizers.